When Nathalie Cabrol was little, her grandfather gave her a pair of binoculars he had picked up as a soldier in Germany after the liberation of France. It was her first real glimpse at the wonders of the moon and stars. “Later,” Cabrol says with a laugh, “my toys became more elaborate and complex.”

Today she uses robots to hunt for alien life. Cabrol is a planetary geologist and astrobiologist at the SETI Institute’s Carl Sagan Center and NASA’s Ames Research Center, both in Mountain View, Cal...